Reversed-phase high-performance liquid chromatography of catecholamines and their congeners with simple acids as ion-pairing reagents.

We have investigated the value of various common acids as ion-pairing reagents for high-efficiency separations of catecholamines and their metabolites in reversed-phase high-performance liquid chromatography. The retention of norepinephrine, alpha-methylnorepinephrine, dopamine, alpha-methyldopamine, L-dopa, alpha-methyldopa, dihydroxybenzylamine, epinephrine, carbidopa and DOPAC was measured in mobile phases composed of nitric, sulfuric, acetic and trichloroacetic acids at pH 2-5 and anion concentrations ranging from 5-500 mM. The solute capacity ratios were dependent on the hydrophobicity and concentration of the ion-pairing reagent and the pH of the mobile phase. Good retention, peak symmetry and high efficiency (3000 theoretical plates for 300 mm) was found for mobile phases composed of the strong inorganic acids and trichloroacetic acid. Chromatography was compared to that seen using the detergent sodium octylsulfate. Trichloroacetic acid gave retention and efficiency similar to sodium octylsulfate. These experiments show that simple acids can replace alkylsulfates as ion-pairing reagents for the separation of the catecholamines and their metabolites.